The next big breakthrough in your family history might be found not in microfilm but in microbiology. Here's how DNA is putting the gene in genealogy.

Sometimes, records and oral histories aren't enough. Every genealogist smacks into brick walls, feels the chill of a paper trail run cold, hears family tales of famous lineages but can't prove them. Many of us wonder about the cousins out there we haven't met yet, and may never get to. But these traditional roadblocks don't have to bring your research to a standstill anymore. There's a new frontier, brimming with new answers, that genealogists are just beginning to explore: genetic genealogy. By examining the stuff of our genes, scientists are able to tell whether one person shares an ancestor with another, about how long ago that common ancestor lived, and even his ancient ancestral homeland. DNA testing is bringing people of the same ancestry together from across the globe, showing us where our forebears migrated from, and eliminating dead ends by revealing whom we're not related to.

A few years ago, the Internet was the "next big thing" for family historians because it allowed them to connect with relatives like never before and to discover information they might not have otherwise found. But DNA testing is quickly taking over as the hot new tool for genealogists. "DNA is a record of who we are and how we're related to each other," says Scott Woodward, who heads the Center for Molecular Genealogy at Brigham Young University. "DNA can identify an individual, link him to a family and identify extended family groups (tribes or clans)." Its accuracy in determining family relationships is unparalleled, and DNA's potential to build a global genealogy database is mind-boggling.

Clarke Glennon of Merion Station, Pa., (glenneil@bellatlantic.net) realized this potential after coordinating a DNA study of 23 Glennon males in the United States and Ireland. He'd spent many years using traditional genealogical methods to research his family history, but hit a dead end with his great-great-grandparents in 1845 Glinsk, County Galway, Ireland — a common problem for Irish family historians. He'd heard about the idea of using the Y chromosome, the part of genes that's passed only from father to son, to show if men with the same surname are connected by the same ancestor. He had himself tested, then convinced other Glennons to contribute their DNA.